Wood residue comes from different sources ranging from natural debris on the forest floor to man-made residues from activities such as forest management (thinning and pruning), harvesting, transporting, dry land sorting and sawmill processing of lumber. In particular, the wood residue generated by forest harvesting, transporting the trees to mills, and sorting is mainly formed of split, broken and rejected logs, tree tops, limbs and branches. Wood residue generated by sawmill processing is generally in the form of slabs, edgings and trimmings. All of the above wood residues are characterized by pieces with highly irregular shapes and variable dimensions. Wood residues tend to be collected into loose piles of jumbled and tangled pieces that are difficult to handle and sort as will be described below.
Traditionally, the portion of the wood residues classified as "good, clean fiber" is chipped and sold for pulp. While wood residue from forest management activities is processed by mobile equipment, the rest is handled by dedicated fixed machinery such as chippers and hogs. Due to problems with the handling, sorting and processing of wood residues, the remainder of the wood residues are burned for fuel or dumped to landfill. However, increasing public pressure due to environmental concerns has resulted in federal and local regulators attempting to discourage the waste of wood residues by taking steps to issue fewer burning permits, enacting tighter air quality control and emission requirements and restricting land usage. These steps have prompted the forest industry to take another look at wood residues, which are becoming more and more of a liability, with a view to converting the residues more completely to a source of fiber.
A major step toward the efficient conversion of more wood residues to usable material such as wood flakes or other value added wood fibers is the development of appropriate machinery for effective sorting and handling of the irregularly shaped and dimensioned wood residue. By processing wood residues, additional value is extracted from what was formerly wood waste which will improve a mill's recovery factor and directly influence its profitability.
In the past, various handling and sorting systems have been developed to handle non-uniform materials.
U.S. Pat. No. 2,753,976 to Fitzmaurice discloses an aligning conveyor which relies on a series of conveyor rollers rotating at successively faster speeds to align articles on the conveyor.
U.S. Pat. No. 4,440,287 to Lund et al. discloses an aligning apparatus for wood flakes.
U.S. Pat. No. 4,826,388 to Bielagus discloses an apparatus for sorting material by length that relies on articles of a defined length passing through gaps between adjacent conveyor rollers.
U.S. Pat. No. 5,363,950 to Lacuna et al. discloses a lumber organizer having drums that are rotated at a greater speed than the infeed conveyor to align the lumber.
The following patents disclose further examples of material handling equipment:
U.S. Pat. No. 4,494,919 to Knudson et al.
U.S. Pat. No. 4,666,029 to Burkner
U.S. Pat. No. 5,325,954 to Crittenden et al.
U.S. Pat. No. 5,404,990 to Barnes et al.
None of the apparatus and techniques disclosed in the foregoing references is particularly well suited to sorting materials such as wood residues formed from a random collection of tangled and jumbled irregular, elongate pieces.